In a 5-4 decision the court said that the coverage formula used by the government to determine which states are required to get federal permission before they make any changes to voting laws is unconstitutional. The ruling effectively puts the issue back in the hands of lawmakers to revise the law. And until then, the ruling effectively renders section five of the Voting Rights Act inoperable.

"Our country has changed, and while any racial discrimination in voting is too much, Congress must ensure that the legislation it passes to remedy that problem speaks to current conditions," wrote Chief Justice John Roberts in the court's opinion.

The decision came down along partisan lines, with conservative justices Roberts, Antonin Scalia, Anthony M. Kennedy, Clarence Thomas, and Samuel Alito making up the majority.

The court left standing Section 5 of the law, a key section that requires states with a history of voter discrimination to have any changes to voting rules approved by federal officials, but strikes down the coverage formula used to choose which states should be covered.

"We issue no holding on section 5 itself, only on the coverage formula. Congress may draft another formula based on current conditions," Roberts said.

Justice Ruth Bader Ginsburg wrote a dissent joined by Justice Kagan, Breyer, and Sotomayor.

"Just as buildings in California have a greater need to be earthquake-proofed, places where there is greater racial polarization in voting have a greater need for prophylactic measures to prevent purposeful race discrimination," Ginsburg took the unusual step of reading her dissent from the bench.

Critics say that Congress ignored prior warnings from the Court about the continued constitutionality of some sections of the law.

"If Congress had updated the coverage formula to use registration and turnout data from the 2004 election, none of the states currently subject to Section 5 would have remained covered because the registration and turnout of black voters is on par with white voters and exceeds that of white voters in some of the covered states," said Hans von Spakovsky, senior legal fellow at the Heritage Foundation. "It is a victim of its own success and is no longer needed. Despite claims to the contrary, Americans will continue to be protected from discrimination by the other permanent provisions of the Voting Rights Act."

Supporters of the law fear that Congress—with its deepening partisan divide-- will not act.

Jon Greenbaum, chief counsel of the Lawyers' Committee for Civil Rights Under Law expressed dismay.

"The Supreme Court has effectively gutted one of the nation's most important and effective civil rights laws," Greenbaum said. "Minority voters in places with a record of discrimination are now at greater risk of being disenfranchised than they have been in decades. Today's decision is a blow to democracy. Jurisdictions will be able to enact policies which prevent minorities from voting, and the only recourse these citizens will have will be expensive and time-consuming litigation."

The Voting Rights Act was signed into law in 1965 by President Lyndon Johnson and aimed at discriminatory voting practices such as literacy tests once used by some Southern states. It was passed after "Bloody Sunday," when protestors urging voting rights protections were beaten while trying to march from Selma to Montgomery, Ala.

At issue in the case was whether Congress was right in 2006 to reauthorize the expiring sections of the law for 25 more years.

Roberts lashes out at Congress for reauthorizing the law using a dated coverage formula.

"There is no denying, however, that the conditions that originally justified these measures no longer characterize voting in the covered jurisdictions. By 2009, the racial gap in voter registration and turnout was lower in the States originally covered by Section 5 than it was nationwide," Roberts wrote. "At the same time, voting discrimination still exists; no one doubts that. The question is whether the Act's extraordinary measures, including its disparate treatment of the States, continue to satisfy constitutional requirements. "

Thomas went much further than his colleagues, saying that he would have struck section 5 of the law.

"While the Court claims to issue no holding on section 5 itself, its own opinion compellingly demonstrates that Congress has failed to justify current burdens with a record demonstrating current needs," Thomas wrote. "By leaving the inevitable conclusion unstated, the Court needlessly prolongs the demise of that provision."

Lawyers for Shelby County, Ala., a covered jurisdiction under the VRA, argued that Congress was wrong in 2006 to reauthorize extend the provision. They argued that "things have changed in the South" and that the mostly Southern states covered by Section 5 should no longer be subject to a law that exacts a "heavy, unprecedented federalism cost" absent a widespread and persisting pattern of constitutional violations.

The jurisdictions covered under the law include Alabama, Alaska, Arizona, Georgia, Louisiana, Mississippi, South Carolina, Texas and Virginia as well as portions of California, Florida, Michigan, New York, North Carolina and South Dakota.

In reauthorizing the Act in 2006, Congress held 21 hearings, heard testimony from witnesses and amassed more than 15,000 pages of evidence. The vote was 98-0 in the Senate and 390-33 in the House.

In court briefs, Solicitor General Donald B. Verrilli Jr. argued that "Congress made the considered judgment in 2006 (as it had in 1970, 1975 and 1982) that covered jurisdictions continue to resist minority voters' equal enjoyment of the right to participate in the political process."

A lower court upheld Section 5, ruling that Congress, "after assembling and analyzing an extensive record, made its decision: Section 5's work is not yet done."

The decision was penned by Roberts, who as a young lawyer in the Reagan Justice Department argued to limit the reach of the law. In 2009, the Supreme Court heard a related case and Roberts warned that some members of the court had "serious misgivings" about the constitutionality of Section 5.